Water-Pipe Corrosion

Q: It wasn't long after we moved into our newly constructed house that the copper water-supply pipes started to leak. This has happened four separate times since then. The leaks tend to occur in the pipes at or near soldered fittings. Neither my builder nor my plumber has been able to figure out what's causing the leaks, and none of my neighbors are having problems with their pipes. Our water comes from a municipal source, not a well. What's going on?

By plumbing and heating expert Richard Trethewey of This Old House magazine

Q:

It wasn't long after we moved into our newly constructed house that the copper water-supply pipes started to leak. This has happened four separate times since then. The leaks tend to occur in the pipes at or near soldered fittings. Neither my builder nor my plumber has been able to figure out what's causing the leaks, and none of my neighbors are having problems with their pipes. Our water comes from a municipal source, not a well. What's going on?
— Dan Meyer , Maineville, Ohio

A:

Richard Trethewey replies: Generally, leaks in copper pipe can be traced back to a problem with the way the pipes were installed or to the water itself. For instance, flux—the acidic paste used in soldering—react with copper if the pipes stand idle for a long period after installation. This kind of trouble typically crops up near fittings and in cold-water pipes because hot water is better at washing flux away. Also, if a pipe wasn't reamed after being cut, the burr on the inside will cause turbulence—tiny swirls of water so vigorous that they actually wear away the metal. Too much velocity, either from undersized pipes or excessive water pressure, can have the same effect.

Then there's the water itself. Anything abrasive, such as bits of rust or any other contaminant, will scour the inside of the pipe and exacerbate the effects of turbulence and velocity. So-called "aggressive," or acidic, water with a pH of 6.8 or less will eat through copper. Water loaded with dissolved minerals can generate copper-dissolving electrical charges.

Since your neighbors aren't having the same problem, I'd rule out water chemistry, for now. The only way to determine exactly what's causing the leaks is a laboratory test. Start by contacting the Copper Development Association (copper.org). With your bad pipe in hand, their experts may be able to uncover the source of the failures or help you find a forensic engineering firm that specializes in corrosion analysis.